This invention relates to the preparation of useful aromatic polyethers, and more particularly to the preparation of aromatic polyethers with improved solvent resistance and reduced melting temperatures, yet with thermally-reversible cross-linking properties, resulting from the grafting of crystallizable polyester segments onto the polyether backbone.
Aromatic polyethers, also well known as polyphenylene oxides, are a class of polymeric materials which have been used in a wide variety of applications. However, they have certain deficiencies which detract from their usefulness. For instance, they are soluble in several common solvents, including the halocarbon and aromatic hydrocarbon types of paint thinners and removers. This solvent sensitivity can limit their use in structural articles which must be painted and repainted. Furthermore, the popular commercially available polyether, poly(2,6-dimethylphenylene oxide), is a very high melting plastic, and as such, is more difficult to fabricate into finished parts than is desired. Traditionally, attempts to improve the solvent resistance of thermoplastics have involved the incorporation of certain thermosettable chemical entities, such as acetylenic groups, onto the base polymer, thus eliminating the thermoplastic nature of the polymer and at the same time converting it to a solvent resistant material. However, that approach, which has not yet been accomplished for aromatic polyethers, has the disadvantage of being irreversible, so that it is not possible to reprocess the crosslinked polymer.
Efforts to reduce the melting temperature of polyphenylene oxides have, for the most part, centered on blending lower softening or melting polymers with the polyether to give resin mixtures which can be processed at an overall lower temperature than the polyether by itself. While this method can give some improvement, it also compromises the ultimate properties of the polyphenylene oxide, causing its use to be limited to much lower temperatures. That method also fails to improve the solvent sensitivity of the polyphenylene oxide.
Polyphenylene oxide compositions have been disclosed by Schmukler in U.S. Pat. No. 3,396,146. Schmukler discloses a polyphenylene oxide which has a repeating unit containing a single aromatic ring substituted with two monovalent substituents. This differs from the present invention in two significant ways. First, the repeating unit of the present invention contains three forms of aromatic rings in varying proportions including the unmodified polyphenylene oxide unit and two modified polyphenylene oxide units. Second, the present invention has polypivalolactone grafts which are not present in the Schmukler polymer.
Hay, in U.S. Pat. No. 3,402,143 also discloses polyphenylene oxide compositions. This reference is distinguishable on the same grounds as is the Schmukler patent.
A process for producing graft copolymers comprising polyphenylene ether is disclosed by Miyashita, et al. in U.S. Pat. No. 4,456,736. This graft polymerization does not include the use of polypivalolactone grafts of the present invention. Also, the method of producing these graft copolymers as described by Miyashita, et al. is significantly different from the process of the present invention.
All of these prior art patents suffer from the disadvantage that they do not describe a product which has the desirable properties possessed by the composition of the present invention. Accordingly, the present invention represents a significant advance over the prior art.